In semiconductor processing, ion implantation processing of semiconductor substrates is necessary. In the processing, an ion beam emitted from an ion source is accelerated or decelerated to a predetermined energy by an accelerating tube, and converged by quadrupole lenses to irradiate the substrate. In order to implant the ions in the substrate uniformly, the ion beam is scanned while the irradiation is performed.
FIG. 8A and FIG. 8B are explanatory diagrams of the spatial distribution and scanning distance of an ion beam. An ion beam 2 radiated on a semiconductor substrate W has a current density with a spatial distribution D. In order to perform ion implantation uniformly over the whole region of the substrate W, it is necessary to scan until the spatial distribution D of the ion beam falls outside of the substrate. As shown in FIG. 8A, in the case where the spatial distribution D1 of the ion beam is small, the scanning distance L1 of the ion beam becomes short, and as shown FIG. 8B, while in the case where the spatial distribution D2 of the ion beam is large, the scanning distance L2 of the ion beam becomes long. If the scanning distance is short, the ion implantation time becomes short, and thereby improving the throughput. Therefore, a smaller spatial distribution of the ion beam is preferable.
On the other hand, the greater the current density of the ion beam, the shorter the implantation time becomes. However, the greater the current density, the more the ion beam diverges due to the space charge effect, which increases the spatial distribution. Therefore, it is necessary to compress the spatial distribution by setting the operating conditions of the optical elements, while maintaining the current density of the ion beam by setting the operating conditions of the ion source. Heretofore, compressing the spatial distribution has been achieved by manually changing the operating conditions of an accelerating tube and quadrupole lenses, or the like, while monitoring the spatial distribution in the vicinity of the substrate.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. S63-91949
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H05-135729